1. Field of the Invention
The present invention relates to the preparation of doped pentasil-type zeolites using doped seeds.
2. Prior Art
U.S. Pat. No. 5,232,675 discloses a process for the preparation of rare earth metal (RE)-doped pentasil-type zeolites using RE-doped faujasite seeds. This process leads to the crystallisation of pentasil-type zeolite on the faujasite-type seeds. Hence, the product consists of two types of zeolites one within the other: a core of RE-doped faujasite and a shell of pentasil-type zeolite. So, the RE-ions are located in the core and not (or at least not significantly) in the pentasil-type shell. This will hinder the RE-ions from improving the activity, selectivity, and stability of the pentasil-type zeolite.
Furthermore, upon thermal treatment (e.g. during calcination, steaming, or use in an FCC unit), the RE-ions move to the very small sodalite cages of the faujasite zeolite, thereby further decreasing their influence on the activity, selectivity, and stability of the pentasil-type zeolite.
The present invention offers a process for the preparation of doped pentasil-type zeolites in which the dopant is not just located in the core.